Deeply understand the analysis of greedy mode and non-greedy mode of JS regular expressions

This article mainly introduces the analysis of greedy mode and non-greedy mode for in-depth understanding of JS regular expressions. It has certain reference value. Now I share it with you. Friends in need can refer to it

The greedy mode

mentioned regular quantifiers before, but the quantifiers will bring about the problem of which should be matched.

The following regular expression:

\d{3,6}

This regular expression matches 3 to 6 numbers, but when this regular expression is used to match the

12345678 string , should it match three numbers, six numbers, or neither?

You can try it first:

let text = '12345678'
let reg = /\d{3,6}/g
text.replace(reg, 'X')      // X78

You can see that this regular expression replaces the six numbers

123456 with X, that is, in normal mode , the regular expression will match as many matches as possible.

Under normal circumstances, regular expressions adopt greedy mode, that is, match as many as possible.

Non-greedy mode

However, sometimes we need the regular expression to match as few as possible, that is, once a successful match is made, no more attempts will be made. This is the non-greedy mode. So, how to enter non-greedy mode?

The method is very simple, just add

? after the quantifier.

let text = '12345678'
let reg = /\d{3,6}?/g
text.replace(reg, 'X')      // X45678

It can be found that in non-greedy mode, this regular pattern only matches

123, which is the minimum match.

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